Fertilization is the process of fusion of two types of gametes (spermatozoan and ovum) so as to form a diploid zygote. In human beings, fertilization takes place mostly in the ampullary isthmus junction of the oviduct (Fallopian tube).The oocycte can live for 72 hours but can fertilized only during the first 24 hours of this period. Ovum takes 12-24 hours to reach the site of fertilization.

Functions of Fertilization

1. It restores the diploid number of chromosomes, characteristics of the species viz., 46 in human being.

2. Fertilization initiates cleavage.

3. Fertilization results in determination of sex in the embryo.

4. It introduces the centrioles which are lacking in the mature egg.

5. Fertilization membrane developed after the entry of the sperm prevents the entry of other sperms into the ovum.

6. It brings together the chromosomes and genes from two different lines of ancestry and results in new genetic recombination, which ensures improved adaptation to ever changing environment.

When sperm reaches the ovum in the oviduct it releases a substances known as antifertilizin. It is an acid protein secreted by the acrosome. At the same time, the ovum releases another chemical substance known as fertilizin. It is a glycoprotein. Fertilizin reacts with the antifertilizin in a manner similar to antigen antibody reaction. The fertilizin-antifertilizin reaction is specific and this makes a path for the sperm to reach the surface of the ovum.

The adhesion of spermatozoon to the egg surface occurs due to the presence of fertilizin molecules in the surface layer of egg cytoplasm, which receive antifertilizin molecules present on the surface of spermatozoon.Function of Fertilizin:1. Makes the sperm sticky so that they adhere into clumps.2. Leads to the capacitation of sperm, enabling it to penetrate the egg surface.3. Makes sperm to adhere to the surface of egg and ensures fertilization.4. Clumping or agglutination of sperm thins out the number of spermatozoa around the egg to check the entry of any additional sperm into the egg.

The placenta is the physiological connection between the mother and the foetus. In human, the placenta is referred to as chorioallantoic placenta. The placenta is formed of chronion (foetal part) and decidua basalis (maternal part). The chorion penetrates deep into the uterine wall with its chorionic villi. So the degree of intimacy between the maternal and foetus tissue is great. At the time of birth of uterine tissue is lost along with foetal membranes. This type of placenta is known as haemochorial placenta. The umbilical cord connects the foetus to the placeta.

Functions of Placenta

1. It acts as a barrier between the foetus and the mother.2. It acts as an ultrafilter.3. Soluble inorganic and organic materials, nutrients, hormones, antibodies against diptheria, small pox, scarlet fever, measles etc, can pass through the placenta from mother to foetus.4. It helps in the exchange of gases between the mother and the foetus.5. It helps in the elimination of nitrogenous discharges and other wastes of the foetus.6. It acts as an endocrine gland and produces hormones such as HCG(Human Chorionic Gonadotropin), chorionic thyrotropin, chorionic corticotropin, chorionic somatomammotropin, estrogens and progesterone. It also secretes progesterone until the end of pregnancy. At the time of parturition, the placenta secretes relaxin, which helps in the relaxation of pubic ligaments to enable birth of the child.

Two key classes of regulatory molecules, cyclins and cyclin dependent kinases (CDKs), determine a cell’s progress through the cell cycle. Cyclins form the regulatory subunits of an activated heterodimer; cyclins have no catalytic activity and CDKs are inactive in the absence of partner cyclin. When activated by a bound cyclin, CDKs perform a common biochemical reaction called phosphorylation that activates or inactivates target proteins to orchestrate coordinated entry into the next phase of the cell cycle.

Different cyclin-CDK combinations determine the downstream targeted proteins. CDKs are constitutively expressed in cells whereas cyclins are synthesised at specific stages of the cell cycle, in response to various molecular signals.

Food is any substance which when taken into the body serves to provide materials for liberation of energy, body structure maintenance, repair, growth of tissues, development, reproduction and resistance to diseases. Most of our food elements are complex organic molecules. The major components of food are carbohydrates, proteins, fats, vitamins, minerals and water. The plant cellulose is the principal source of carbohydrates for many herbivorous animals. Man and other animals, subsisting cereal grains, fruits, and tubers, take carbohydrates mainly in the form of starch. Most human beings are omnivorous in diet and take vegetables as well as animal foods in the cooked form.

Functions of Food

1. Energy: Components of food function as respiratory substrates (glucose). They liberate energy required by the body to carryout numerous life functions.

2. Growth: Components of digested food build up new protoplasm and new cells for growth.

3. Structure: Components of food get converted into absorbable state during digestion. The same are absorbed and transported to different parts of the body for assimilation. The assimilated materials form various components of the body like bone, skin, muscles etc.

4. Repair: Food provides materials for repair of injured and old tissues.

5. Replacement: A very large number of cells die out daily in the body. They are replaced by newly formed cells. Formation of new cells requires food materials.

6. Formation of hormone and enzymes: Food provides materials for manufacture of regulatory substances like hormones and enzymes.

7. Immunity: Antibodies, antitoxins and some WBC (white blood corpuscles) are involved in maintenance of immune system of the body against attack from pathogens. They are produced from food materials.

The secretion of liver is known as bile. Bile is a clear golden yellow or greenish fluid. It is alkaline in a nature. A normal man secretes about 500 ml to 1 litre in 24 hours. The bile is stored in gall bladder. The capacity of gall bladder is 40-60 ml. Gall bladder is absent in animals such as whale, horses, rats etc.

The bile in the gall bladder is concentrated by the reabsorption of water, bicarbonates, chlorides and sodium. Hence the bile from the liver and that from the gall bladder is slightly different. Bile contains bile salts (sodium and potassium salts of glycochoic and taurocholic acids), bile pigments such as bilirubin (yellow) and biliverdin (green), cholesterol, lecithine, alkaline phosphatase etc.Normal level of bilirubin is 0.2 - 1.2 mg/ 100ml of blood.An increase in level of bile pigment in the blood causes Jaundice. In jaundice no emulsification of fat takes place, so digestion of fat is not completed and the unabsorbed fat appears in the faeces. The bile reaches the duodenum through bile duct. The bile duct is formed by the union of the common hepatic duct and cystic ducts which joins with the pancreatic duct before opening into the duodenum. Most of the functions of bile are due to the presence of bile salts. The following are the major functions of bile salts.

Functions of Bile

1. They are necessary for the digestion and absorption of fats. They activate pancreatic lipase and help in emulsification of food fats and their absorption in the intestine.2. They keep cholesterol in solution in the bile.3. They have a mild purgative action.

Scientific names are formal, universally accepted names that obey rules
and regulations for naming of plants and animals provided by the International
Code of Botanical Nomenclature (ICBN) or International Commission on Zoological
Nomenclature (ICZN). Binomial
nomenclature system is followed in which a scientific name has two parts or
epithets; generic epithet and specific epithet followed by author citation
(Abbreviation of the author who published the name first). Author citation is
optional but often advisable. Eg: Mangifera indica Linn. for
mango tree.

Why we need
scientific names instead of vernacular or common names?

Limitations of
common names

An organism can have multiple common
names

Vary from country to country or
within state or locality.

Known by people of one region,
language or country

Name available for only relatively
few plant and animal species

Not universal, not regulated by any
constituted authority

Non specific and often misleading “ring
worm” is not a worm. It is a fungus. Jelly fish is not a fish

Why scientific
names are useful in taxonomy?

An universally accepted name and
understood globally

Each organism identified has a
unique scientific name

Scientific name seldom changes

Scientific names are often descriptive and logical and suggest some
information about animal or a plant. Example: Thunbergia grandiflora (grandiflora=large flowered)

Scientific names are based on set of rules stipulated by ICBN and
ICZN. It brings order to nomenclature (naming of organism)

A complete Definition of
Photosynthesis: An anabolic process by which chloroplast of green plants and
other phototroph’s synthesize carbohydrates (glucose) and evolve molecular O2
as by-product, using CO2, H2O and sunlight.

Till 1930, it was believed that
photosynthesis is just the reverse of respiration.

An
experiment conducted by Ruben, Randall and kamen (1940) proved that O2
evolved during photosynthesis comes from water, not from CO2.

For the
experiment, they used heavy radioisotopes of Oxygen (O18) in water
(H2O18) and CO218

Experiment 1:
When photosynthesis occurs in the presence of H2O18 and normal CO2, the heavy isotope
was found in the evolved O2

Experiment 2:
When photosynthesis occurs in the presence of normal H2O and CO218, the isotopic
oxygen is not evolved.

The experiment
for the first time proved that the oxygen evolved during photosynthesis comes
from water.

Original paper

Then the
conventional equation was modified as 6 molecules of H2O is not
sufficient for the evolution of 6 molecules of O2.